As part of a multi-center grant we will attempt to prevent the development of NIDDM in 200 subjects with impaired glucose tolerance. The overall study will involve 20 clinical centers and 4000 subjects. This proposal will take seven years, with a one year protocol development, five year clinical trial and one year evaluation period. The proposed intervention will be a factorial design with one factor being diet and exercise versus usual cre and the second factor being an insulin sensitizer (e.g. Metformin) versus placebo. The primary endpoint will be the development of NIDDM. Secondary endpoints include changes in lipids, lipoproteins, ankle/arm ratio, urinary albumin and carotid wall thickness. Subjects will be obtained by several methods including: a) community advertising through radio and television advertisements; b) selective screening based on blood glucose from the Brady Green clinic; and c) subjects from the San Antonio Heart Study. Subjects identified with newly discovered diabetes but with normal fasting glycemia (2-hr glucose greater than or equal to 200 mg/dl, but fasting glucose <140 mg/dl) will be entered into a parallel secondary prevention trial to prevent the development of fasting hyperglycemia. In addition to the endpoints for the subjects in the primary prevention trial, these subjects will have assessment for diabetic neuropathy and retinopathy.